That bracket part is not a common replacement item, as it has no moving parts. The pins and rubber boots should be available.
The problem you observe is not unusual. Generally you can just clean and lube, and get on with things.
Unless the pins are scored or pitted badly, they can usually be polished up with green abrasive pad or emery cloth, cleaned, and put back into service. If the rubber boots are not torn, you can usually pull them out and clean them out with brake cleaner.
I use silicone grease for this application. Holds up well.
Unfortunately, you have probably replaced calipers that were not part of the original problem.
Best of luck.
1986 300E 5-Speed 240k mi.